The following generally relates to electric paper. It finds particular application to using anisotropic conductive islands with electric paper. However, other applications are also contemplated.
Electric paper commonly is defined as any electronically-addressable display medium that approximates paper in form and function. Typically, electric paper is relatively light-weight, thin and flexible, and it should display images virtually indefinitely while consuming minimal power. In addition, electric paper should be reusable. Thus, it should be erasable and/or re-writeable. Images typically are displayed using reflected light and accommodate relatively wide viewing angles.
A known sheet and display system (“Gyricon”) is disclosed in various patents and articles, such as U.S. Pat. No. 4,126,854 by Sheridon titled “Twisting Ball Display.” The Gyricon display system is comprised of an elastomeric host layer of approximately 300 micrometers thick which is heavily loaded with rotating elements, possibly spheres, tens of micrometers (e.g. 100 micrometers) in diameter. Each rotating element has halves of contrasting colors, such as a white half and a black half. Each bichromal rotating element also possesses an electric dipole, nominally orthogonal to the plane that divides the two colored halves. Each bichromal rotating element is contained in its own cavity filled with a dielectric liquid. Upon application of an electric field between electrodes located on opposite surfaces of the host layer, the rotating elements will rotate depending on the polarity of the field, presenting one or the other colored half to an observer. Other known systems use color rotating elements in which each element includes one or more colors. Likewise, the polarity of the field determines which color presented to the observer.
A Gyricon sheet has many of the requisite characteristics of electric paper, namely, bistable image retention, wide viewing angle, thin and flexible packaging, and high reflectance and resolution. U.S. Pat. No. 5,389,945 issued to Sheridon on Feb. 14, 1995, and titled “Writing System Including Paper-Like Digitally Addressed Media and Addressing Device Therefor,” describes an electric paper printing system that employs independent, external addressing means to put images on the Gyricon sheets. The external addressing means is described as a one-dimensional array of electrodes connected, either directly or by wireless technology, to modulating electronics. As the one-dimensional array is scanned across the sheet, modulating electronics adjust the potential at the individual electrodes, creating electric fields between the electrodes and an equipotential surface. An image is created in the sheet according to the polarity of the electric fields.
Recent embodiments of these sheets usually incorporate charge-retaining islands thereon. Such embodiments are described in U.S. Pat. No. 6,235,395 B1, issued Apr. 24, 2001 and entitled “Charge Retention Islands for Electric Paper and Applications Thereof.” In U.S. Pat. No. 6,235,395 B1, the Gyricon sheet is comprised of a first encapsulating layer patterned with conductive charge-retaining islands, a second encapsulating layer that may or may not be patterned with charge-retaining islands, and a sheet positioned there between. The first and second encapsulating layers include at least one transparent window through which the sheet can be viewed and provide at least one external surface patterned with charge retaining islands that can be stimulated with an external charge transfer device.
The charge-retaining islands typically are square and organized in a two-dimensional array. Channels of insulating material separate the charge-retaining islands. The channels serve to isolate the charge-retaining islands and should be small with respect to the charge-retaining islands so that the maximum possible area of the display is covered with conductive charge-retaining material. In one conventional technique, charge-retaining islands are created from conductive and transparent Indium Tin Oxide (ITO) on a transparent polyester film. The polyester is coated with a very thin layer of ITO, and then channels are etched in the ITO by photolithographic processes well known in the art. The remaining conductive ITO regions act as charge retaining islands, while insulating channels are created by the underlying polyester.
Typically, the charge-retaining islands are attached to a conductive island plane of the electric paper. As a consequence, one or more of the plurality of conductive islands can become separated from the electric paper. For example, wear associated with folding and/or crumbling the electric paper can result in detachment of one or more of the plurality of conductive islands from the conductive island plane. In another example, repeated folding can result in conductive island detachment from the conductive island plane. In view of at least the above-noted deficiencies with conventional electric paper, there is an unresolved need for new and improved electric paper and associated methods for forming the new and improved electric paper.